Field of the Invention
The present invention relates to a so-called film heating-type image heating device configured to heat a developer image on a recording material and an image forming apparatus including the same.
Description of the Related Art
A conventional image heating device of this kind is for example known from Japanese Patent Application Laid-open No. 04-44075. More specifically, the known device includes a flexible film (tubular rotating member), a heating member provided slidably at an inner circumference of the film, a pressure roller (pressure member) that nips the film between the heating member and itself to form a pressure-contact nip portion. The pressure-contact nip portion nips and transports a recording material having a toner image formed thereon, and the toner image is fixed on the recording material by heat from the heating member and pressure force by the pressure-contact nip portion.
The temperature of the heating member is detected by a temperature detecting element provided at a surface of the heating member on the opposite side to the pressure-contact nip portion and controlled at a prescribed temperature.
In the meantime, Japanese Patent Application Laid-open No. 05-27619 suggests such a film-heating type image heating device in which a lubricant is interposed between a film and a heating member in order to secure slidability between the film and the heating member.
The lubricant is desirably applied uniformly on the inner surface of the film but it is a general practice in manufacturing to apply the lubricant on the surface of the heating member.
However, when the lubricant is applied on the heating member and rotation of the film is not sufficient, a large amount of the lubricant may be left sticking on the heating member during, for instance, shipment of the product. The presence of much lubricating grease between the heating member and the film prevents transmission of heat from the heating member to the film, and therefore the heating member can be easily heated to high temperatures.
As a result, when the temperature is controlled in response to a temperature detected at a surface of the heating member different from the sliding surface of the film, electric power provided to the heating member is reduced, and therefore the amount of heat generation is reduced. In this way, the amount of heat transmitted to the recording material is also reduced, so that toner may not be sufficiently melted, in other words, a heating failure may result. A reduction in the amount of the lubricant may reduce such a failure but then the friction between the film and the heating member increases, which may cause slipping between the film and the recording material.